As a gift, Dilhan was given the number n=1^{1} \cdot 2^{2} \cdots 2021^{2021}, and each day, he has been dividing n by 2021! exactly once. One day, when he did this, he discovered that, for the first time, n was no longer an integer, but instead a reduced fraction of the form \frac{a}{b}. What is the sum of all distinct prime factors of b?